Train parallax computer



Nov. 20, 1951 F. l.. HEREFORD, JR., Erm. 2,575,956

TRAIN PARALLAX COMPUTER 2 SHEETS-SHEET l Filed April 27, 1948 Olulolllilllvllt INVENTORS. FRANK L. HEREFORD. JR. WALTER D- wHrIEEA D1VJ W# ATTORNEY Patented Nov. 20, 1951 TRAIN PARALLAX COMPUTER Frank L. Hereford, Jr., Swarthmore, Pa., and

Walter D. Whitehead, Jr., Old Church, Va., assignors to United States of America as represented by the Secretary oi the Navy Application April 27, 1948, Serial No. 23,475

1 claim. 1

The present invention relates to train parallax correctors.

More particularly, it relates to apparatus which determines and transmits to a gun the angular obtained from the present description and the accompanying drawings illustrating two specic embodiments thereof. In said drawings;

Figure 1 is a block diagram of the apparatuses (Cl. 23S-61.5)

- Figure 2 is a circuit diagram of an amplifier thatiorms a-partof the device; and

Figure 3 is a block diagram, similar in general to Figure l, but showing a modiiied form.

correction in train due to parallactic error intro- 5 The present invention provides an automatic duced by the distance between the gun and its means for correcting the error due to train pardirector. allax, existing whenever there is a distance be- An object of the invention is to eliminate the tween the gun director and the gun controlled train parallax error, that otherwise would exist, and which will be serious whenever the director when a gun and its director are not at substanand the gun are at widely separated locations tially the same point, by introducing the neceson a vessel. sary correction for parallax into the gun signal. In connection with the aiming or pointing The object of a modified form of the invention, of guns, it is customary to use devices known as also disclosed herein, is to correct for the future computers, which are electrically operated derange of the target, instead of the range at the vices for deriving voltages that represent the time of firing, by introducing a proper train angles .pg in train, and 0g in elevation, of the gun, parallax correction. in terms of certain of their trigonometric func- All these problems are solved automatically by tions, conveniently the sine of (pg, and cosine of the train parallax corrector, which not only com- 0g. These computers are well known in the art, putes the proper angular correction, but also and in and of themselves constitute no novel automatically adds it to the gun orders. features. Hence their mechanical and electrical It is easy to see that this correction for train structures are not discussed herein, and mere parallax will increase directly as the separation block diagrams are employed instead. of the gun from its director, but will decrease, Another apparatus used in pointing a gun is inversely, with the range, that is, it will become known as a wind box and has the purpose of smaller for a more distant target, as long as the correcting the data obtained from the computers. range is large compared to said separation. It to allow for the dei'lecting effect, on the projectile, can also be shown that the train parallactic of the natural wind, and/or the relative motion` error increases with the train angle, and inof the ship carrying the gun, with respect to the creases also with increasing elevation angle. The air. This device is likewise well known and will relation is expressed mathematically in the folbe indicated here merely by a block diagram, lowing paragraph: marked source of cos 0g, which is the measure When the base line between gun and director of one of the voltage-outputs it yields. has the length b, in yards, and 0g designates ele- A third auxiliary apparatus found in gun vation angles and sbg train angles, of the gun, the 3,-, director installations is the range-repeater, latter being measured in aclockwise direction, which includes a dial mounted on a shaft that when seen from above, zero train angle in the rotates whenever the range of the target is case of a ship being the forward direction along changing, and is controlled electrically to keep in the fore-and-aft line of the ship, the correction synchronism with a manually-rotated shaft of a. iS gil/@11,111 degrees, by thev equation: 40 radar range-iinding apparatus. This range- A b repeater shaft is also employed in connection FM with the present invention and is likewise shown R COS 9# merely as a block diagram, suitably labeled. for any range R. When a definite base line is Referring first t0 Figure 1 there is Shown an e e assumed, say 10o yards, 573e becomes 5730. 4:; input circuit l, 2 to which is Supplied a voltage The' present-errmemputer" assumesA that --pfoertonai t0 R @CHQ-Thiswltageeasalready e I voltages proportional respectively to sin rpg and explained, is here obtained from the voltage repcos 0g, and rotary motion (inversely) proporresentng COS 0g yielded by the Wind bOX. by tional to the range R, are avauabl feeding this voltage across a 1,000 ohm poten- A clear understanding of the invention may be 5o tiometer, not Shown the movable element 0f which is operated by the present range shaft in the range repeater box. A potentiometer 3, 26 having a resistance of the order of 50,000 ohms, is bridged across the wiresi and 2, as is also a circuit consisting ofA the'resistors 4 and 5 in series,

and circuits;

each of about 50,000 ohms, to the junction of which is connected the wire 6, which is thus a center tap, the potential of which corresponds to that of the mid-point of potentiometer resistor 3.

A voltage proportional to sin g is obtained from the computer, as already stated, and is fed to the wires 6a. and 1. A series resistor 8, of 5,000 ohms, is placed in one of these leads and a 2,000 ohm potentiometer 9, I is bridged across them as shown. The slider I0, connected to wire II, bears on the potentiometer resistor 9 and is brought to such position of adjustment that the voltage between wire 6 and wire II represents b sin g.

The amplifier I3 has a power supply I4 energized from the mains as shown. This amplifier supplies one phase of a two-phase alternating current motor I1 through the output leads I5 and 'to the amplifier I3 to zero.

I6 of said amplifier. The other phase of the motor I1 is supplied with properly phased alternating current at a suitable voltage, say 20 volts, derived from the mains and transformed in voltage and adjusted in phase angle by the phase network I8 which has the output leads I9 and 20. The details of a suitable amplifier are disclosed in Figure 2.

The motor I1 will run in one direction or the other, as determined by the lag or lead of the amplifier output with respect to the output from thenetwork I8. The shaft 2I of the motor I1 operates the generator 22 directly, and through the gear box 23 and shaft 25 also operates the synchro-generator 24 and the arm 26 of the potentiometer 3. The motor I1 thus adjusts the potentiometer 3 into balance, by reducing the input The generator 22, which has an exciting winding energized by leads I and 2, through a suitable resistor 11, prevents hunting by opposing the necessary small signal to the amplifier input to prevent overrunning of the motor I1. This signal is thus proportional to the voltage across leads I and 2 multiplied by the speed of shaft 2I of motor I1.

The synchro-generator 24 derives its eld excitation from the alternating current mains, as indicated on the drawing, and yields an output through the set of three leads, marked I2 pa, which is fed to the gun director, not shown. This is the nal output of the present device.

The amplifier, which is designated as a whole by reference character I3 in Figure 1, is shown in detail in Figure 2. It comprises four thermionic tubes, arranged in three stages. The rst two tubes, 30 and 3I, may suitably be twin triodes, such as type 6SC7. The nal or power output stage includes preferably two beam-power tubes 32 and 33 connected in push-pull. Type 6V6 is indicated on the drawings as suitable.

The input to the amplifier is fed to it through wires II and 21, and the direct current power through wires 28 and 29 from the power supply I4, while the output of the amplifier is delivered through wires I and I6. AS suitable values for all the circuit elements are suggested on the drawing, it isnot necessary to go into further detail here.

The equation solved by the above described parallax corrector, namely:

. is based upon the assumption that R represents the present range Rp of the target. Actually the equation yields the correct values of m only if R represents'the "future range of the target 4 (l. e., the range at the time of impact of the projectile). This future range Rf is given by the empirical relation:

is the time rate of change of the range. A rotary motion proportional to the value of is available in the range-repeater apparatus, as previously stated. The coeicient 1.2 in the above formula is empirical, and provides correction for the fact that usually the range of the target is decreasing, so that the parallax error angle increases more rapidly than would be accounted for by a unity coefficient.

The revised circuit, shown in Figure 3, enables the instrument to solve the modied equation:

Here the voltage from the wind box, proportional to cos 0g, is fed into terminals 34 and 35 of one transformer 4I of a Scott transformer system in the range apparatus (lO-to-l step down) which has taps on the secondary winding 40 from which may be obtained the voltages desired. Across taps 36 and 31 is placed a 10 ohm potentiometer 38 with a sliding contact 61 which is operated by the range rate shaft 39. The proper choice of voltage taps on the transformer yields a voltage as shown, proportional to dR (i4-1.2E

This voltage is fed across a ohm potentiometer 42 with a sliding contact 68 actuated by the present range shaft 43, and asa consequence We have across the conductors 44 and 45 a voltage proportional to Ths voltage is supplied from the range apparatus.

It is introduced into the parallax unit, shown rto the right of the vertical dashed line, through conductors 44 and 45 which feed it across a 1to1 isolating transformer 46. A 100 ohm balancing potentiometer 41 is provided between the two secondary windings 48 and 49 and the total secondary voltage is applied across a 2,000 ohm potentiometer 50 having a sliding contact 69 operated by the 361) shaft 5I of the computer. Thus the voltage across the tap on the balancing potentiometer 41 and the potentiometer 50 is proportional to:

The voltage from the pg computer, proportional to sin qhg, is introduced into another transformer 52 of the Scott transformer system (lO-to-l step down) through conductors 53 and 54 as shown. The output of winding 55 of this transformer feeds into the parallax unit through another l-to-l isolating transformer 58 through conductors 56' and 51. Connected across the o utvoltage produced by generator 22.

put winding 59 of this transformer, is a resistance-capacitance circuit 13, 14, which combines a phase shifter and an amplitude control, including resistors and 16. The contact 60 provides a means of shifting the phase of the sin pg voltage in order that it may be exactly 180 out of phase with the voltage across sliding contacts 6I and 69. The contact 62 on the 2,000 ohm potentiometer 10 provides means of making the voltage output of this net-work proportional to b sin og.

It will be seen that the circuits just described include a plurality of voltage dividers, namely, resistors 10, 13, 'I5 and 16 together with the sliding contacts movable thereover, and that all of these means jointly also constitute a voltage dividing means in the sense in which this term is used in the claim.

Two 5,000 ohm resistors 63 and 64 provide a voltage divider, the resistor 64 being connected across the input side of the amplifier I3. The amplifier design may be identical wathethat shown in Figure 2. Two other changes are embodied in the modied computer: first, a 5,000 ohm resistor 1I and-a .5 mfd. capacitor 12 are placed in series with the input or field-energizing leads to the generator 22 to insure proper phasing of its output; second, the synchro-generator 24 of Fig. l turning through 12m. is replaced by two differential synchro-generators, one 65 turning through p, the other 66 through 36m. The gear train is changed accordingly, the modified gear box 23a, through shaft 25h, causing the former 1211,. potentiometer, and the differential synchrogenerator 66 now to turn instead through 36m, and additionally through shaft 25a causing the differential synchro-generator 65 to turn through m.

In this modified form the two differential synchro-generators 65 and 66 replace the synchro-generator 24 of the originally described form. Each of these differential synchro-generators receives an input through the set of three input conductors entering at its lower edge and yields an output through the corresponding set of three output conductors leaving at its upper edge. The inputs are derived from corresponding synchro-generators in the fire-control system, not shown, and the outputs lead to the gun director system, likewise not illustrated.

The remainder of the instrument is identical with that described previously.

The operation of the apparatus will be understood from its detailed description, but for convenience may be summarized as follows:

Referring first to the simpler form shown in Figs. 1 and 2, a signal proportional to R cos 0g in amplitude, and having the input frequency determined by the power source, say 60 cycles per second, is introduced across the voltage divider 3 from the wind box. The generator 22 is also supplied with the same signal, as field excitation.

Tapped across the signal input conductors I and 2 are the two equal resistors 4 and 5 in series connection', whereby a neutral point between said conductors isxestablishedftoreceive-a-second signal, namely the voltage difference existing between conductors 6 and II, as determined by the position of slider I0 on resistor 9, the signal representing sin qg, derived from the computer, being impressed across resistor 9.

Thus there exists in the amplifier input circuit the voltage between leads II and 26, ,from these two sources in series. However, there is also the w producing-meansrsaid-seconebresister having-aais proportional, on the one hand, to the field excitation of the generator, which is derived from the same leads I and 2 that supply the voltage R cos 0g to the voltage divider 3, and, on the other hand, is proportional to the rotational speed of the driving motor I1. 'I'he output voltage of this generator 22 is however opposed to the other two voltages in series therewith, and thus the input signal voltage supplied to the amplifier I3 is reduced thereby.

Through the gear box 23, the motor shaft 2 I also operates the synchro-generator 24, and the arm 26 of the voltage divider 3, at a reduced speed, until a balance is attained, that is, until the voltage fed to the amplifier input terminals is reduced to zero. The voltage of the generator 22 assists in thus reducing the signal input voltage and thereby provides damping and prevents hunting or overshooting the zero position. The synchro-generator 24 yields the nal output of 4the whole system, that is, the parallax-corrected gun order, which is supplied to the gun director system.

The operation of the Fig. 3 form is substantiallythe same as that of the one just described,

with the exception that this system makes it possible to point the gun so that the missile will strike at he anticipated future position of a moving target. This is accomplished by means of the range-rate shaft 38 in cooperation with the present-range shaft 43, as already described. Due to the addition of shaft 39 and the potentiometer 38 controlled thereby, it becomes possi- `ble to provide a signal component representing a future value of the range and direction of the target, and to combine this with the other signals to produce the required pointing of the gun. The two differential synchro-generators 65, and B6 here supply the outputs of the device, which are fed to the gun director system.

Having disclosed the invention by describing a simplified form thereof, together with a preferred but more elaborate modification, it should be understood that this disclosure is provided solely for purposes of illustration and not as a limitation of the invention to all or any of the details thereof. The invention is defined solely in and by the following claim.

We claim:

In a parallax corrector for a gun, means for electrically producing an alternating voltage representative of the cosine of the elevation angle of the gun, a resistor having a sliding contact movable thereover, connections from said means to the terminals of said resistor to maintain across said resistor a voltage representative of the cosine of said elevation angle, rate responsive means connected to said contact for generating an alternating voltage that is a function of the range rate of the target, mechanical connections where' by said rate responsive means moves said contact over the resistor, a second resistor having one terminal electrically connected to said contact and having its other terminal electrically connected to a fixed point of said elevation voltage sliding contact movable thereover, range responsive means mechanically moving said last named contact in accordance with the range of the target thus providing a modified alternating voltage proportional to the product of the range, a function of range rate and the cosine of the angle of elevation, means for electrically producing an alternating voltage representative of the sine of This Voltage the train angle of the gun, voltage dividing means electrically connected to combine said modified voltage with a predetermined portion of said train angle voltage, thus producing a control voltage that is proportional to the product of the range, a, function of range rate and the cosine of the angle of elevation, a potentiometer across which said control voltage is applied, an amplifier for said control voltage, and servo mechanism controlled by the output of said ampler and including a motor and a generator operated thereby, for adjusting said potentiometer and for generating a voltage representative of the parallax correction.

FRANK L. HEREFORD, J R.

WALTER D. WHITEHEAD, J a.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Lovell et al. Sept. 4, 1946 Hull et al. Jan. 14, 1947 Haynes June 3, 1947 Knowles Oct. 7, 1947 Holden Oct. 14, 1947 Campbell Oct. 28, 1947 Lakatos Jan. 13, 1948 Lovell et a1 June 22, 1948 

